Method of producing gray-iron castings



Patented. Aug. 10, 1926.

UNITED STATES PATENT OFFICE.

DANIEL H. MELOCHE, OF DETROIT, MICHIGAN, ASSIGNOR TO EARL HOLLEY, OF

DETROIT, MICHIGAN. 4

i METHOD OF PRODUCING GRAY-IRON CASTINGS.

No Drawing. Applicationflled January 81, 1924, Serial No. 689,816. Renewed November 30, 1925.

This invention relates to the method. of producing gray iron castings of a superior quality.

W'hen gray iron is cast in sand molds a 1 characteristic structure is produced in which large crystals of graphite exists in a matrix of ferrite. This iron is soft, easily machinable, and of good wearing qualities. Millions of tons of this iron are cast every ear. y This iron, however, exhibits strength in neither compression nor tension and is easily broken by impact. There is a demand therefore for an iron having all the good qualities of gray iron, together with greater strength and resistance to impact.

When iron is cast in a heated metal mold protected with a refractory lining and a superimposed coating of lampblack, as described in my N 0. 623,053, allowed October 17th, 1923, the iron produced thereby has the good qualities of gray iron but is not markedly superior to gray iron in strength and resistance to impact.

I have discovered, however, that if I anneal such an iron at 1550 F. for one hour, that whilst the characteristic structure of such iron is unchanged the strength is increased 100%. On the other hand, if the annealing is continued at this temperature for two or three hours the characteristic structureis destroyed and the iron is weaker than ordinary sand cast iron.

.The explanation ofthis remarkable in- 1crease in strength is believed to be as folows:

When gray iron, containing over 2.2% silicon and over 2.5% carbon (preferably 2.75% silicon, 3.25% carbon, and 0.6% manganese), is cast "in heated metal'molds, protected as described above, whilst the initial rate of cooling is checked the average rate of cooling is greater than when using sand co-pending application Serial than 2.2% silicon and more than 2.5% carmolds, the result being that the silicon preci itates out the carbon as minute particles 0 graphite entirely surrounded by ferrite.

The specific gravity of graphite being but of the specific gravity of pure iron (ferrite) the'volume of the mass increases at the moment of precipitation, the result being that each particle of graphite is surrounded by an envelope of ferrite in tension and there are therefore casting strains uniformly distributed throughout the iron, and 5 itis to relieve these casting strains that the short anneal of one hour at 1550 is used rather than a longer anneal.

.It will be noted that this anneal is not intended to change either the chemical colnposition or physical appearance of the casting. However, the anneal actually does cause some of the combined carbon that has escaped the effect of the silicon to come out of solution. This is not intended however. Generally speaking, there is no material change in the structure. a What I claim is: 1. Tlidmethod of makinggray-iron castings consisting of casting such iron in a heated metal mold protected with aheat insulating refractory and a superimposed coating of lam blaclg removing the casting from said mo d and heating the casting above 1475 F. and below 1600 F. long 76 enough to relieve the casting strains and not long enough to destroy the characteristic structure of the' iron.

2. A gray iron casting containing more bon, characterized by the uniform distribution of of the carbon as particles of graphite surrounded by ferrite, annealed so as-to relieve the casting-strains and so as not to materially change the characteristic 86 structure of the metal.-

1 In testimony whereof I afiix my signature. DANIEL H. MELOCHE. 

